Bile acids and bile salts are synthesized from cholesterol and play critical roles in preparing dietary triacylglycerols (TAGs) for degradation in the intestine. The properties of bile acids and bile salts help define their functions.
Bile acids are synthesized in the
. The cholesterol substrate has hydroxyl groups added to it and the double bond in the B ring reduced. The most common products are the triol, cholic acid, and the diol, chenodeoxychoic acid, which can be further modified in later steps. These compounds are known as
. The rate-limiting step is the addition of a hydroxyl group to C-7 in the B ring by the enzyme cholesterol-7-$\alpha$-hydroxylase.
This enzyme is up-regulated by the presence of cholesterol and down-regulated by the presence of
. Before the bile acids leave the organ where their synthesis occurs, they are conjugated to a molecule of either glycine or taurine to produce bile salts. Bile salts have ionizable side groups; thus, the bile salt molecule overall is